The present invention is directed, in general, to a semiconductor wafer polishing apparatus and, more specifically, to a carrier head equipped with controllable struts that enable the force applied to the carrier head by each strut to be individually controlled.
In the manufacture of microcircuit dies, chemical/mechanical polishing (CMP) is used to provide smooth topography on a substrate of a semiconductor wafers. A conventional wafer polishing apparatus comprises a carrier head, a carrier gimbal, a drive shaft, and a polishing platen. A semiconductor wafer is held within the carrier head while rotational and downward forces are applied to the semiconductor wafer through the drive shaft and against a polishing platen. The carrier gimbal is designed to allow for deviations from the horizontal between a wafer surface being polished and the polishing platen surface. The gimbal is effectively a universal joint between the drive shaft and the carrier head. Should there be a deviation of the platen surface from the horizontal at any point, the gimbal allows the carrier head to follow the contour of the local surface by tilting appropriately on either or both of two orthogonal, essentially-horizontal axes.
One problem that exists with the conventional gimbal design is that the gimbal design simply distributes the vertical force applied to the drive shaft to the surface of the semiconductor wafer. Therefore, if a given wafer is slightly thicker at one point on its edge than at another point, the thickness difference may persist as the planarization continues. That is, the gimbal assists in correcting local irregularities of the wafer surface, but does not correct for global irregularities of the semiconductor wafer.
Also, the nature of a given wafer may be that it planarizes faster in one sector than another. This results in a similar situation as described above, i.e., the semiconductor die on one sector of the wafer may be thinner or thicker than those on another sector of the same wafer.
Accordingly, what is needed in the art is an apparatus that permits adjustment of localized thickness of a semiconductor wafer for greater uniformity of the planarity of the semiconductor wafer during CMP.
To address the above-discussed deficiencies of the prior art, the present invention provides a polishing apparatus comprising a carrier head, rigid members coupled to the carrier head at different points on the carrier head, and a controller coupled to each of the rigid members wherein the controller is configured to regulate forces applied against the carrier head through each of the rigid members.
Thus, in a general sense, the present invention provides a polishing apparatus having a carrier head coupled to a drive system through rigid members that may be used to regulate forces applied against the carrier head at different points to more uniformly polish semiconductor wafers.
In one embodiment, the rigid members are struts. In an advantageous embodiment, the polishing apparatus further comprises sensors coupled to the carrier head proximate each of the different points and are configured to sense a force applied to the carrier head at each of the different points. In other embodiments, the sensors may be pressure sensors, force sensors, capacitance sensors, resistance sensors, or piezoelectric sensors. In another embodiment, the polishing apparatus further comprises a thickness sensor configured to sense a thickness of a desired layer on a semiconductor wafer.
Each of the rigid members, in another embodiment, may be coupled to a mechanical screw configured to provide a force against the carrier head. In a further aspect of this embodiment, each of the rigid members includes the mechanical screw. The mechanical screw may be coupled to a motor that provides rotation to the mechanical screw. The motor is preferably coupled to the controller.
In an alternative embodiment, each of the rigid members is coupled to a pneumatic cylinder configured to provide a force against the carrier head. In a further aspect of this embodiment, the pneumatic cylinder is coupled to a pneumatic system that provides the force. In yet another embodiment, each of the rigid members is coupled to a hydraulic cylinder configured to provide a force against the carrier head. The hydraulic cylinder is preferably coupled to a hydraulic system that provides the force.
In another embodiment, each of the rigid members is coupled to a piezoelectric transducer configured to provide a force against the carrier head. The piezoelectric transducer may be coupled to an electrical system either contracts or expands the piezoelectric transducer to provide the force against the carrier head.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.